COALESCE

COALESCE takes any number of arguments and returns the first value that is not null.

COALESCE(x,y,z) = x if x is not NULL
COALESCE(x,y,z) = y if x is NULL and y is not NULL
COALESCE(a,y,z) = z if x and y are NULL but z is not NULL
COALESCE(x,y,z) = NULL if x and y and z are all NULL

schema:gisq

COALESCE can be useful when you want to replace a NULL value with some other value.
In this example you show the name of the party for each MSP that has a party.
For the MSP with no party (such as Canavan, Dennis) you show the string None.

SELECT name, party
,COALESCE(party,'None')AS aff
FROM gisq.msp WHERE name LIKE'C%'

SELECT name, party
,COALESCE(party,'None')AS aff
FROM msp WHERE name LIKE'C%'